The present invention relates to a technology for calculating a recommended route from a starting point to a destination, and suggesting it to a user in an on-board navigation device or the like.
In an on-board navigation device, a technology (a route guidance) has been already put into a practical use, which searches a recommended route from a set starting point to a set destination based on road map data, and guides a vehicle to reach the destination on the recommended route by using a display device, a voice output device and the like.
In the route guidance technology, all routes connecting the set staring point with the set destination are searched by using road map data, and a technology called a dijkstra method searches for a route of minimum cost (for example, the gross distance of the route), thereby setting the searched route as the recommended route. And, for example, the set recommended route is displayed while overlapping a displayed map, and information to be required (for example, information such as whether or not to turn the next intersection) for a vehicle to run on the recommended route is informed via voice. In a case when the vehicle deviates from the recommended route during the route guidance, a recommended route to the destination is searched again, taking the current position of the vehicle as a starting point, and the re-searched route is newly set as the recommended route (an auto-rerouting).
In addition, in an on-board navigation device, in order to position a vehicle on a road in a displayed map, a technology (a map matching) has already been put into a practical use, wherein the current position of the vehicle, determined by various kinds of sensors such as gyro, a running vehicle speed sensor and the like, or GPS receiver, is corrected every specified running distance (for example, 20 meters).
In this map matching technology, the current position of the vehicle, determined by various kinds of sensors such as the running vehicle speed sensor, a gyro or the like, and a GPS receiver, is regarded as a center. Then, all positions corresponding to the current position on the road within a specified range are registered as candidate positions, the specified range being set by the searched current vehicle position, errors included in a traveling direction, and errors of road map data. Then, a current vehicle position is corrected to a candidate position which has the strongest correlation with the current position, in consideration for a distance from a current position to the candidate position; a difference between a vehicle traveling direction, searched by various kinds of sensors such as the vehicle speed sensor, the gyro or the like and the GPS receiver or the like, and a azimuth of road in which a candidate position is set; and a road having the current position of the vehicle corrected by the previous map matching.
Incidentally, in the on-board navigation apparatus to which the foregoing map matching technology is applied, in the case where the plurality of candidate positions are registered, the current position corrected by the map matching at this time is set on a road different from the road with the current position corrected by the previous map matching being set therein (a so-called position skipping). Hereinbelow, a description will be made for this position skipping phenomenon with reference to drawings.
FIG. 5 is a view for explaining the position skipping phenomenon in the on-board navigation apparatus to which the map matching technology is applied. Here, FIG. 5(a) shows an actual road, and FIG. 5(b) shows a shape of a road determined by the road map data corresponding to the road shown in FIG. 5(a).
Now, in FIG. 5(a), it is assumed that the vehicle changes a lane before a junction A and goes straight, then the map matching is performed immediately after the vehicle passes the junction A. In this case, according to the foregoing map matching technology, a position B on a main lane and a position C on a branch lane, which are shown in FIG. 5(b), are registered as candidate positions, both having strong and uncomparable correlations with the current position of the vehicle determined by various kinds of sensors such as a vehicle speed sensor and a gyro, or a GPS receiver and the like. However, when a difference between a traveling direction of the vehicle, searched by the various kinds of sensors such as the vehicle speed sensor and the gyro, or the GPS receiver and the like, and an azimuth of each road in which the candidate position is set is considered, there is a strong possibility that not the candidate position on the branch lane where the vehicle actually runs but the candidate position B on the main lane is selected as a current position after correction.
Here, it is assumed that the current position is corrected to the candidate position B by the map matching, further the vehicle runs thereon. Then, it is assumed that map matching is performed when the vehicle reaches a point D on the branch lane. Also in this case, a position E on the main lane and a position F on the branch lane, which are shown in FIG. 5(b), are registered as candidate positions. However, in consideration for a distance from the current position of the vehicle to the candidate position thereof, which is determined by the various kinds of sensors such as the vehicle speed sensor and the gyro or the GPS receiver and the like; or for a difference between the traveling direction of the vehicle, determined similarly to the above by the various kinds of sensors such as the vehicle speed sensor and the gyro or the GPS receiver and the like, and an azimuth of each road where the candidate position is set, there is a strong possibility that the candidate position F on the branch lane is selected as a current position after correction.
Here, if it is assumed that the current position is corrected to the candidate position F by the map matching, the current position being displayed on the display device is suddenly skipped from the main lane onto the branch lane at the point D. This position skipping phenomenon has a possibility of continuing until a relative distance between the main lane and the branch lane or a difference in shapes between the main lane and the branch lane are made apparent.
Now, when the route guidance technology equipped with the above-described auto-rerouting function is further applied to the on-board navigation apparatus to which the map matching technology involving the position skipping phenomenon as described above is applied, a problem to be described below occurs.
Now, in FIGS. 5(a) and 5(b), it is assumed that a route connecting the main lane through the junction A to the branch lane is selected as a recommended route, and that the route guidance is made so that the vehicle may run on the route. Here, as described above, in the case where the vehicle changes the lane before the junction A and goes straight to pass the junction A, leading to the correction of the current position to the candidate position B on the main lane by the map matching, it results in that the vehicle deviates from the recommended route during the route guidance, thus the auto-rerouting is executed. Specifically, the corrected current position B is set as starting point, a recommended route to the destination is searched again, and the re-searched route is newly set as a recommended route. Thus, the route guidance is performed.
Moreover, as described above, in the case where the map matching is performed when the vehicle reaches the point D on the branch lane, and as a result, the current position is corrected to the candidate position F on the branch lane, it results in that the vehicle deviates from the recommended route searched again by the previous auto-rerouting. Accordingly, the auto-rerouting is executed again. Specifically, the corrected current position F is set as a starting point, a recommended route to the destination is searched again, and the re-searched route is newly set as a recommended route. Thus, the route guidance is performed.
As described above, when the route guidance technology equipped with the auto-rerouting function is applied to the on-board navigation apparatus to which the map matching technology is applied, the auto-rerouting is executed every time when the current position is subjected to the position skipping, and a different recommended route is submitted to the user, which is awfully troublesome.
The present invention was made with the foregoing circumstance in mind. An object of the present invention is to prevent the execution of the auto-rerouting every time when the position skipping is made in a route guidance device such as the on-board navigation apparatus to which the map matching technology is applied.
In order to solve the foregoing subject, the present invention is a route guidance device, in which a recommended route from a set starting point to a set destination is searched to be submitted to a user; and when a current position of a vehicle deviates from the recommended route, a recommended route from the current position of the vehicle to the destination is newly searched to be submitted to the user, the route guidance device comprising:
data storing means for storing road map data;
current position measuring means for measuring a current position of a vehicle;
map matching means for correcting the current position of the vehicle measured, for each specified interval, by the current position measuring means so as to be located on any road in a specified range from the current position among roads determined by the road map data stored in the data storing means; and
auto-rerouting preventing means for preventing a search for a new recommended route from a corrected current position of the vehicle to the destination even if the current position of the vehicle is corrected by the map matching means and deviates from the recommended route resultantly when the current position of the vehicle measured by the current position measuring means is in the vicinity of a junction on the recommended route among the roads determined by the road map data stored in the data storing means.
Here, a judgment as to whether or not the current position of the vehicle measured by the current position measuring means is in the vicinity of the junction on the recommended route among the roads determined by the road map data stored in the data storing means may be performed, for example, in the following manner. Specifically, information regarding the junctions is previously set in the road map data stored in the data storing means, and among the junctions stored in the data storing means, the junction on the recommended route, which is proximate to the current position of the vehicle measured by the current position measuring means, is searched. Then, investigation is made as to whether or not the current position of the vehicle exists within a specified distance from the junction in the traveling direction of the vehicle (for example, the distance is within 1000 m in the case where the recommended route is a highway, and is within 400 m in the case where the recommended route is an open road).
Alternatively, the judgment may be made by investigating whether or not the vehicle moves for a specified distance after the number of roads selected to be within a specified range from the current position of the vehicle measured by the current position measuring means is increased in the map matching. means. In this case, when a value determined by the running distance of the vehicle after it is judged that the current position of the vehicle is in the vicinity of the junction on the recommended route and the azimuth difference among a plurality of roads selected to be within the specified range from the current position of the vehicle measured by the current position measuring means in the map matching means exceeds a predetermined reference value, the current position of the vehicle is corrected by the map matching means, and as a result, the prevention of the search for a new recommended route from the corrected current position of the vehicle to the destination in the case where the vehicle deviates from the recommended route may be released.
According to the present invention, by the foregoing configuration, in the case where the vehicle is located in the vicinity of the junction where there is a strong possibility that the position skipping occurs due to the map matching, the search for the new recommended route from the current position of the vehicle to the destination is prevented even in the case where the vehicle deviates from the recommended route. Therefore, a situation such that the auto-rerouting is executed every time when the current position is subjected to the position skipping, and a different recommended route is submitted to the user can be prevented from occurring.